Giant magnetoresistive sensor with high-resistivity magnetic layers

ABSTRACT

A giant magnetoresistive stack for use in a magnetic read head has a plurality of layers including at least one ferromagnetic layer which contributes to a giant magnetoresistive signal, and at least one doped ferromagnetic layer which does not contribute to a giant magnetoresistive signal. The dopant in the doped ferromagnetic layer reduces parasitic shunting current through the giant magnetoresistive stack by providing an increase in resistivity without a decrease in magnetization.

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority from Provisional Application No.60/305,749, filed Jul. 16, 2001 entitled “Spin Valve with High-ResistiveMagnetic Layers” by C. Hou and O. Heinonen.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to a giantmagnetoresistive sensor for use in a magnetic read head. In particular,the present invention relates to a giant magnetoresistive read sensorhaving an enhanced giant magnetoresistive response.

[0003] Giant magnetoresistive (GMR) read sensors are used in magneticdata storage systems to detect magnetically-encoded information storedon a magnetic data storage medium such as a magnetic disc. Atime-dependent magnetic field from a magnetic medium directly modulatesthe resistivity of the GMR read sensor. A change in resistance of theGMR read sensor can be detected by passing a sense current through theGMR read sensor and measuring the voltage across the GMR read sensor.The resulting signal can be used to recover the encoded information fromthe magnetic medium.

[0004] A typical GMR read sensor configuration is the GMR spin valve, inwhich the GMR read sensor is a multi-layered structure formed of anonmagnetic spacer layer positioned between a synthetic antiferromagnetand a ferromagnetic free layer. The magnetization of the syntheticantiferromagnet is fixed, typically normal to an air bearing surface ofthe GMR read sensor, while the magnetization of the free layer rotatesfreely in response to an external magnetic field. The syntheticantiferromagnet includes a reference layer and a pinned layer which aremagnetically coupled by a coupling layer such that the magnetizationdirection of the reference layer is opposite to the magnetization of thepinned layer. The resistance of the GMR read sensor varies as a functionof an angle formed between the magnetization direction of the free layerand the magnetization direction of the reference layer. Thismulti-layered spin valve configuration allows for a more pronouncedmagnetoresistive effect, i.e. greater sensitivity and higher totalchange in resistance, than is possible with anisotropic magnetoresistive(AMR) read sensors, which generally consist of a single ferromagneticlayer.

[0005] A pinning layer is typically exchange coupled to the pinned layerof the synthetic antiferromagnet to fix the magnetization of the pinnedlayer in a predetermined direction. The pinning layer is typicallyformed of an antiferromagnetic material. In antiferromagnetic materials,the magnetic moments of adjacent atoms point in opposite directions and,thus, there is no net magnetic moment in the material.

[0006] An underlayer is typically used to promote the texture of thepinning layer consequently grown on top of it. The underlayer istypically formed of a ferromagnetic material and is chosen such that itsatomic structure, or arrangement, corresponds with a desiredcrystallographic direction.

[0007] A seed layer is typically used to enhance the grain growth of thelayers consequently grown on top of it. In particular, the seed layerprovides a desired grain structure and size for the underlayer.

[0008] One principal concern in the performance of GMR read sensors isthe ΔR (the maximum absolute change in resistance of the GMR readsensor), which directly affects the GMR ratio. The GMR ratio (themaximum absolute change in resistance of the GMR read sensor divided bythe resistance of the GMR read sensor multiplied by 100%) determines themagnetoresistive effect of the GMR read sensor. Ultimately, a higher GMRratio yields a GMR read sensor with a greater magnetoresistive effectwhich is capable of detecting information from a magnetic medium with ahigher linear density of data.

[0009] A key determinant of the GMR ratio is the amount of parasiticshunting current flowing through the GMR read sensor. The GMR signalproduced by the GMR read sensor is generated by the current flowingthrough the free layer, the spacer layer, and the reference layer of thesynthetic antiferromagnet. Current flowing through any other layer is aparasitic shunting current, and reduces the GMR signal. As a result, theless parasitic shunting current that is present in the GMR read sensor,the greater the GMR ratio. Parasitic shunting current can be reduced byincreasing the resistivity of the layers that do not contribute directlyto the GMR signal. In particular, increasing the resistivities of thepinning layer and the underlayer is especially desirable because theselayers are typically formed of magnetic materials with lowresistivities. In these instances, however, it is important to ensurethat the magnetic properties of these layers are maintained in order forthe GMR read sensor to function properly.

[0010] The present invention addresses these and other needs, and offersother advantages over current devices.

BRIEF SUMMARY OF THE INVENTION

[0011] The present invention is a giant magnetoresistive stack for usein a magnetic read head. The giant magnetoresistive stack has aplurality of layers including at least one ferromagnetic layer whichcontributes to a giant magnetoresistive signal, and at least one dopedferromagnetic layer which does not contribute to a giantmagnetoresistive signal. The dopant in the doped ferromagnetic layerreduces parasitic shunting current through the giant magnetoresistivestack by providing an increase in resistivity without a decrease inmagnetization.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a layer diagram of a first embodiment of a giantmagnetoresistive stack of the present invention.

[0013]FIG. 2 is a bar graph of the GMR ratio of the first embodiment ofa giant magnetoresistive stack of the present invention.

[0014]FIG. 3 is a bar graph of the ΔR of the first embodiment of a giantmagnetoresistive stack of the present invention.

[0015]FIG. 4 is a layer diagram of a second embodiment of a giantmagnetoresistive stack of the present invention.

[0016]FIG. 5 is a layer diagram of a third embodiment of a giantmagnetoresistive stack of the present invention.

DETAILED DESCRIPTION

[0017]FIG. 1 is a layer diagram of a first embodiment of a giantmagnetoresistive (GMR) stack 10 of the present invention. GMR stack 10is configured as a bottom spin valve and includes a seed layer 12, anunderlayer 14, a pinning layer 16, a synthetic antiferromagnet 18, aspacer layer 20, and a free layer 22. Seed layer 12 is preferably NiFeCror Ta. Underlayer 14 is a ferromagnetic material, preferably CoFeX orNiFeX, where X is selected from the group consisting of B, V, Cr, Mo, Wand Ti, and is positioned adjacent to seed layer 12. Pinning layer 16 isan antiferromagnetic material, preferably selected from the groupconsisting of PtMn, IrMn, NiMn, NiO and FeMn, and is positioned adjacentto underlayer 14. Synthetic antiferromagnet 18 includes a ferromagneticpinned layer 24, a ferromagnetic reference layer 28, and a couplinglayer 26 positioned between pinned layer 24 and reference layer 28, andis positioned such that pinned layer 24 is adjacent to pinning layer 16.Coupling layer 26 is preferably ruthenium, reference layer 28 ispreferably CoFe, and pinned layer 24 is preferably CoFeX, where X isselected from the group consisting of B, V, Cr, Mo, W and Ti. Free layer22 is a ferromagnetic material, preferably CoFe or NiFe. Spacer layer 20is a nonmagnetic material, preferably copper, and is positioned betweensynthetic antiferromagnet 18 and free layer 22.

[0018] The magnetization of synthetic antiferromagnet 18 is fixed whilethe magnetization of free layer 22 rotates freely in response to anexternal magnetic field emanating from a magnetic medium. Referencelayer 28 and pinned layer 24 are magnetically coupled by coupling layer26 such that the magnetization direction of reference layer 28 isopposite to the magnetization direction of pinned layer 24. Themagnetization of pinned layer 24 is pinned by exchange coupling pinninglayer 16 with pinned layer 24. Underlayer 14 promotes thecrystallographic texture of pinning layer 16, and seed layer 12 enhancesthe grain growth of underlayer 14. The resistance of GMR stack 10 variesas a function of an angle that is formed between the magnetization offree layer 22 and the magnetization of reference layer 28.

[0019] The GMR signal produced by GMR stack 10 is generated by thecurrent flowing through free layer 22, spacer layer 20, and referencelayer 28. It is therefore desirable to minimize the parasitic shuntingcurrent through the layers of GMR stack 10 that are not responsible forgenerating the GMR signal. As a result, underlayer 14 and pinned layer24 are doped with X, where X is selected from the group consisting of B,V, Cr, Mo, W and Ti, while free layer 22, spacer layer 20, and referencelayer 28 are not doped with X. By doping underlayer 14 and pinned layer24 with X, the resistivities of underlayer 14 and pinned layer 24 aresignificantly increased from about 10 μΩ·cm (without X) to about 100μΩ·cm (with X), while the magnetizations of underlayer 14 and pinnedlayer 24 are maintained at about 2.2 Tesla. In this way, the GMR signalproduced by GMR stack 10 is enhanced and, in particular, the GMR ratioand the ΔR are increased.

[0020] The composition of underlayer 14 when CoFeX is used is preferablyin the range of about [Co(90)Fe(10)]X(>0) to about [Co(90)Fe(10)]X(10),and more preferably in the range of about [Co(90)Fe(10)]X(1) to about[Co(90)Fe(10)]X(3), where the numbers in parentheses represent atomicpercentage, and where the atomic ratio of CoFe in brackets is maintainedwhile the atomic percentage of X is varied. The composition ofunderlayer 14 when NiFeX is used is preferably in the range of about[Ni(80)Fe(20)]X(>0) to about [Ni(80)Fe(20)]X(10), and more preferably inthe range of about [Ni(80)Fe(20)]X(1) to about [Ni(80)Fe(20)]X(3).

[0021] The composition of pinned layer 24 of synthetic antiferromagnet18 is preferably in the range of about [Co(90)Fe(10)]X(>0) to about[Co(90)Fe(10)]X(10), and more preferably in the range of about[Co(90)Fe(10)]X(1) to about [Co(90)Fe(10)]X(3).

[0022]FIG. 2 is a bar graph comparing the GMR ratio of GMR stack 10 ofthe present invention to the GMR ratio of two similar GMR stacks. Bar100 shows the GMR ratio (the maximum absolute change in resistance ofthe GMR read sensor divided by the resistance of the GMR read sensormultiplied by 100%) of GMR stack 10, where underlayer 14 and pinnedlayer 24 of GMR stack 10 are both CoFeV. Bar 102 shows the GMR ratio ofa GMR stack similar to GMR stack 10, except pinned layer 24 is replacedwith a CoFe layer (underlayer 14 remains CoFeV). Bar 104 shows the GMRratio of a GMR stack similar to GMR stack 10, except underlayer 14 andpinned layer 24 are both replaced by CoFe layers. Bar 1100 shows thatthe GMR ratio of GMR stack 10 is 15.49%. Bar 102 shows that if pinnedlayer 24 is replaced with a conventional CoFe layer, the GMR ratio dropsto 15.17%. Bar 104 shows that if both underlayer 14 and pinned layer 24are replaced with conventional CoFe layers, the GMR ratio drops to14.94%.

[0023] The bar graph of FIG. 3 corresponds to the bar graph of FIG. 2,and compares the ΔR of GMR stack 10 of the present invention to the ΔRof two similar GMR stacks. Bar 110 shows the ΔR (the maximum absolutechange in resistance of the GMR read sensor) of GMR stack 10 whereunderlayer 14 and pinned layer 24 of GMR stack 10 are both CoFeV. Bar112 shows the ΔR of a GMR stack similar to GMR stack 10, except pinnedlayer 24 is replaced with a CoFe layer (underlayer 14 remains CoFeV).Bar 114 shows the ΔR of a GMR stack similar to GMR stack 10, exceptunderlayer 14 and pinned layer 24 are both replaced by CoFe layers. Bar110 shows that the ΔR of GMR stack 10 is 3.22 Ω/sq. Bar 112 shows thatif pinned layer 24 is replaced with a conventional CoFe layer, the ΔRdrops to 3.05 Ω/sq. Bar 114 shows that if both underlayer 14 and pinnedlayer 24 are replaced with conventional CoFe layers, the ΔR drops to2.76 Ω/sq.

[0024]FIG. 4 is a layer diagram of a second embodiment of a GMR stack 30of the present invention. GMR stack 30 is configured as a top spin valveand includes a seed layer 32, a free layer 34, a spacer layer 36, asynthetic antiferromagnet 38, and a pinning layer 40. Seed layer 32 ispreferably NiFeCr or Ta. Free layer 34 is a ferromagnetic material,preferably CoFe or NiFe, and is positioned adjacent to seed layer 32.Synthetic antiferromagnet 38 includes a ferromagnetic reference layer42, a ferromagnetic pinned layer 46, and a coupling layer 44 positionedbetween reference layer 42 and pinned layer 46. Reference layer 42 ispreferably CoFe, coupling layer 26 is preferably ruthenium, and pinnedlayer 46 is preferably CoFeX, where X is selected from the groupconsisting of B, V, Cr, Mo, W, and Ti. Pinning layer 40 is anantiferromagnetic material, preferably selected from the groupconsisting of PtMn, IrMn, NiMn, NiO and FeMn, and is positioned adjacentto pinned layer 46 of synthetic antiferromagnet 38. Spacer layer 36 is anonmagnetic material, preferably copper, and is positioned between freelayer 34 and synthetic antiferromagnet 38.

[0025] The magnetization of synthetic antiferromagnet 38 is fixed whilethe magnetization of free layer 34 rotates freely in response to anexternal magnetic field emanating from a magnetic medium. Referencelayer 42 and pinned layer 46 are magnetically coupled by coupling layer44 such that the magnetization direction of reference layer 42 isopposite to the magnetization direction of pinned layer 46. Themagnetization of pinned layer 46 is pinned by exchange coupling pinninglayer 40 with pinned layer 46. Seed layer 32 promotes thecrystallographic texture and enhances the grain growth of free layer 34.The resistance of GMR stack 30 varies as a function of an angle that isformed between the magnetization of free layer 34 and the magnetizationof reference layer 42.

[0026] The GMR signal produced by GMR stack 30 is generated by thecurrent flowing through free layer 34, spacer layer 36, and referencelayer 42. It is therefore desirable to minimize the parasitic shuntingcurrent through the layers of GMR stack 30 that are not responsible forgenerating the GMR signal. As a result, pinned layer 46 is doped with X,where X is selected from the group consisting of B, V, Cr, Mo, W and Ti,while free layer 34, spacer layer 36, and reference layer 42 are notdoped with X. By doping pinned layer 46 with X, the resistivity ofpinned layer 46 is significantly increased from about 10 μΩ·cm (withoutX) to about 100 μΩ·cm (with X), while the magnetization of pinned layer46 is maintained at about 2.2 Tesla. In this way, the GMR signalproduced by GMR stack 30 is enhanced and, in particular, the GMR ratioand the ΔR are increased.

[0027] The composition of pinned layer 46 of synthetic antiferromagnet38 is preferably in the range of about [Co(90)Fe(10)]X(>0) to about[Co(90)Fe(10)]X(10), and more preferably in the range of about[Co(90)Fe(10)]X(1) to about [Co(90)Fe(10)]X(3).

[0028]FIG. 5 is a layer diagram of a third embodiment of a giantmagnetoresistive (GMR) stack 50 of the present invention. GMR stack 50is configured as a dual spin valve and includes a seed layer 52, anunderlayer 54, a first pinning layer 56, a first syntheticantiferromagnet 58, a first spacer layer 60, a free layer 62, a secondspacer layer 64, a second synthetic antiferromagnet 66, and a secondpinning layer 68. Seed layer 52 is preferably NiFeCr or Ta. Underlayer54 is a ferromagnetic material, preferably CoFeX or NiFeX, where X isselected from the group consisting of B, V, Cr, Mo, W, and Ti, and ispositioned adjacent to seed layer 52. First pinning layer 56 is anantiferromagnetic material, preferably selected from the groupconsisting of PtMn, IrMn, NiMn, NiO and FeMn, and is positioned adjacentto underlayer 54. First synthetic antiferromagnet 58 includes aferromagnetic pinned layer 70, a ferromagnetic reference layer 74, and acoupling layer 72 positioned between pinned layer 70 and reference layer74, and is positioned such that pinned layer 70 is adjacent to firstpinning layer 56. Coupling layer 72 is preferably ruthenium, referencelayer 74 is preferably CoFe, and pinned layer 70 is preferably CoFeX,where X is selected from the group consisting of B, V, Cr, Mo, W, andTi. Free layer 62 is a ferromagnetic material, preferably CoFe or NiFe.First spacer layer 60 is a nonmagnetic material, preferably copper, andis positioned between first synthetic antiferromagnet 58 and free layer62. Second synthetic antiferromagnet 66 includes a ferromagneticreference layer 76, a ferromagnetic pinned layer 80, and a couplinglayer 78 positioned between reference layer 76 and pinned layer 80.Reference layer 76 is preferably CoFe, coupling layer 78 is preferablyruthenium, and pinned layer 80 is preferably CoFeX, where X is selectedfrom the group consisting of B, V, Cr, Mo, W, and Ti. Second pinninglayer 68 is an antiferromagnetic material, preferably selected from thegroup consisting of PtMn, IrMn, NiMn, NiO and FeMn, and is positionedadjacent to pinned layer 80 of second synthetic antiferromagnet 66.Second spacer layer 64 is a nonmagnetic material, preferably copper, andis positioned between free layer 62 and second synthetic antiferromagnet66.

[0029] The magnetizations of first and second synthetic antiferromagnets58 and 66 are fixed while the magnetization of free layer 62 rotatesfreely in response to an external magnetic field emanating from amagnetic medium. Reference layer 74 and pinned layer 70 are magneticallycoupled by coupling layer 72 such that the magnetization direction ofreference layer 74 is opposite to the magnetization direction of pinnedlayer 70. The magnetization of pinned layer 70 is pinned by exchangecoupling first pinning layer 56 with pinned layer 70. Underlayer 54promotes the crystallographic texture of first pinning layer 56, andseed layer 52 enhances the grain growth of underlayer 54. Referencelayer 76 and pinned layer 80 are magnetically coupled by coupling layer78 such that the magnetization direction of reference layer 76 isopposite to the magnetization direction of pinned layer 80. Themagnetization of pinned layer 80 is pinned by exchange coupling secondpinning layer 68 with pinned layer 80. The resistance of GMR stack 50varies as a function of the angles that are formed between themagnetization of free layer 62 and the magnetizations of referencelayers 74 and 76.

[0030] The GMR signal produced by GMR stack 50 is generated by thecurrent flowing through free layer 62, spacer layers 60 and 64, andreference layers 74 and 76. It is therefore desirable to minimize theparasitic shunting current through the layers of GMR stack 50 that arenot responsible for generating the GMR signal. As a result, underlayer54 and pinned layers 70 and 80 are doped with X, where X is selectedfrom the group consisting of B, V, Cr, Mo, W and Ti, while free layer62, spacer layers 60 and 64, and reference layers 74 and 76 are notdoped with X. By doping underlayer 54 and pinned layers 70 and 80 withX, the resistivities of underlayer 54 and pinned layers 70 and 80 aresignificantly increased from about 10 μΩ·cm (without X) to about 100μΩ·cm (with X), while the magnetizations of underlayer 54 and pinnedlayers 70 and 80 are maintained at about 2.2 Tesla. In this way, the GMRsignal produced by GMR stack 50 is enhanced and, in particular, the GMRratio and the ΔR are increased.

[0031] The composition of underlayer 54 when CoFeX is used is preferablyin the range of about [Co(90)Fe(10)]X(>0) to about [Co(90)Fe(10)]X(10),and more preferably in the range of about [Co(90)Fe(10)]X(1) to about[Co(90)Fe(10)]X(3). The composition of underlayer 54 when NiFeX is usedis preferably in the range of about [Ni(80)Fe(20)]X(>0) to about[Ni(80)Fe(20)]X(10), and more preferably in the range of about[Ni(80)Fe(20)]X(1) to about [Ni(80)Fe(20)]X(3).

[0032] The composition of pinned layer 70 of first syntheticantiferromagnet 58 is preferably in the range of about[Co(90)Fe(10)]X(>0) to about [Co(90)Fe(10)]X(10), and more preferably inthe range of about [Co(90)Fe(10)]X(1) to about [Co(90)Fe(10)]X(3).Similarly, the composition of pinned layer 80 of second syntheticantiferromagnet 66 is preferably in the range of about[Co(90)Fe(10)]X(>0) to about [Co(90)Fe(10)]X(10), and more preferably inthe range of about [Co(90)Fe(10)]X(1) to about [Co(90)Fe(10)]X(3).

[0033] In summary, the present invention introduces a GMR read sensorwith at least one doped ferromagnetic layer which does not contribute toa GMR signal. The doped ferromagnetic layer reduces parasitic shuntingcurrent, and thus enhances the GMR response of the GMR read sensor. Thedopant in the doped ferromagnetic layer is preferably selected from thegroup consisting of B, V, Cr, Mo, W, and Ti. The doped ferromagneticlayer may be a pinned layer, an S underlayer, or some other layer whichdoes not contribute to a GMR signal. As a result, the present inventionallows the resistivities of the ferromagnetic layers which do notcontribute to a GMR signal to be increased without increasing theresistivities of the ferromagnetic layers which do contribute to a GMRsignal. Furthermore, the present invention allows the resistivities ofthe ferromagnetic layers which do not contribute to a GMR signal to beincreased without decreasing the magnetizations of these layers.

[0034] Although the present invention has been described with referenceto preferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. A read sensor for use in a magnetic read head, the read sensorcomprising: a giant magnetoresistive stack having a plurality of layers;and means for reducing parasitic shunting current through the giantmagnetoresistive stack.
 2. The read sensor of claim 1 wherein the meansfor reducing parasitic shunting current provides an increase inresistivity without a decrease in magnetization.
 3. The read sensor ofclaim 2 wherein the means for reducing parasitic shunting currentincludes a dopant in a pinned layer, wherein the dopant is selected fromthe group consisting of B, V, Cr, Mo, W, and Ti.
 4. The read sensor ofclaim 3 wherein an atomic percentage of the dopant in the pinned layeris in the range of greater than 0 to about
 10. 5. The read sensor ofclaim 2 wherein the means for reducing parasitic shunting currentincludes a dopant in an underlayer, wherein the dopant is selected fromthe group consisting of B, V, Cr, Mo, W, and Ti.
 6. The read sensor ofclaim 5 wherein an atomic percentage of the dopant in the underlayer isin the range of greater than 0 to about
 10. 7. The read sensor of claim2 wherein the increase in resistivity is about a factor of
 10. 8. Theread sensor of claim 2 wherein the resistivity is about 100 μΩ·cm.
 9. Agiant magnetoresistive stack for use in a magnetic read head, the giantmagnetoresistive stack having a plurality of layers including: aferromagnetic layer which contributes to a giant magnetoresistivesignal; and a doped ferromagnetic layer which does not contribute to agiant magnetoresistive signal.
 10. The giant magnetoresistive stack ofclaim 9 wherein a resistivity of the doped ferromagnetic layer is about10 times greater than a resistivity of the ferromagnetic layer withoutdoping.
 11. The giant magnetoresistive stack of claim 9 wherein aresistivity of the doped ferromagnetic layer is about 100 μΩ·cm.
 12. Thegiant magnetoresistive stack of claim 9 wherein the doped ferromagneticlayer is doped with a dopant which provides an increase in resistivitywithout a decrease in magnetization.
 13. The giant magnetoresistivestack of claim 12 wherein the dopant is selected from the groupconsisting of B, V, Cr, Mo, W, and Ti.
 14. The giant magnetoresistivestack of claim 13 wherein an atomic percentage of the dopant in thedoped ferromagnetic layer is in the range of greater than 0 to about 10.15. The giant magnetoresistive stack of claim 12 wherein the increase inresistivity is about a factor of
 10. 16. The giant magnetoresistivestack of claim 12 wherein the resistivity is about 100 μΩ·cm.
 17. Agiant magnetoresistive stack for use in a magnetic read head, the giantmagnetoresistive stack comprising: a ferromagnetic free layer having arotatable magnetic moment; a first synthetic antiferromagnet comprising:a ferromagnetic reference layer having a fixed magnetic moment; a dopedferromagnetic pinned layer, wherein the pinned layer is doped with adopant selected from the group consisting of B, V, Cr, Mo, W, and Ti;and a coupling layer positioned between the reference layer and thepinned layer; a first nonmagnetic spacer layer positioned between thefree layer and the first synthetic antiferromagnet; and a firstantiferromagnetic pinning layer positioned adjacent to the firstsynthetic antiferromagnet.
 18. The giant magnetoresistive stack of claim17 wherein the doped ferromagnetic pinned layer of the first syntheticantiferromagnet is CoFeX, wherein X is the dopant.
 19. The giantmagnetoresistive stack of claim 18 wherein an atomic percentage of X inthe CoFeX pinned layer of the first synthetic antiferromagnet is in therange of greater than 0 to about
 10. 20. The giant magnetoresistivestack of claim 17 and further comprising: a doped ferromagneticunderlayer positioned adjacent to the first pinning layer, wherein theunderlayer is doped with a dopant selected from the group consisting ofB, V, Cr, Mo, W, and Ti; and a seed layer positioned adjacent to theunderlayer.
 21. The giant magnetoresistive stack of claim 20 wherein thedoped ferromagnetic underlayer is CoFeX, wherein X is the dopant. 22.The giant magnetoresistive stack of claim 21 wherein an atomicpercentage of X in the CoFeX underlayer is in the range of greater than0 to about
 10. 23. The giant magnetoresistive stack of claim 20 whereinthe doped ferromagnetic underlayer is NiFeX, wherein X is the dopant.24. The giant magnetoresistive stack of claim 23 wherein an atomicpercentage of X in the NiFeX underlayer is in the range of greater than0 to about
 10. 25. The giant magnetoresistive stack of claim 17 andfurther comprising: a second synthetic antiferromagnet comprising: aferromagnetic reference layer having a fixed magnetic moment; a dopedferromagnetic pinned layer, wherein the pinned layer is doped with adopant selected from the group consisting of B, V, Cr, Mo, W, and Ti;and a coupling layer positioned between the reference layer and thepinned layer; a second nonmagnetic spacer layer positioned between thefree layer and the second synthetic antiferromagnet; and a secondantiferromagnetic pinning layer positioned adjacent to the secondsynthetic antiferromagnet.
 26. The giant magnetoresistive stack of claim25 wherein the doped ferromagnetic pinned layer of the second syntheticantiferromagnet is CoFeX, wherein X is the dopant.
 27. The giantmagnetoresistive stack of claim 26 wherein an atomic percentage of X inthe CoFeX pinned layer of the second synthetic antiferromagnet is in therange of greater than 0 to about
 10. 28. The giant magnetoresistivestack of claim 25 and further comprising: a doped ferromagneticunderlayer positioned adjacent to the first pinning layer, wherein theunderlayer is doped with a dopant selected from the group consisting ofB, V, Cr, Mo, W, and Ti; and a seed layer positioned adjacent to theunderlayer.
 29. The giant magnetoresistive stack of claim 28 wherein thedoped ferromagnetic underlayer is CoFeX, wherein X is the dopant. 30.The giant magnetoresistive stack of claim 29 wherein an atomicpercentage of X in the CoFeX underlayer is in the range of greater than0 to about
 10. 31. The giant magnetoresistive stack of claim 28 whereinthe doped ferromagnetic underlayer is NiFeX, wherein X is the dopant.32. The giant magnetoresistive stack of claim 31 wherein an atomicpercentage of X in the NiFeX underlayer is in the range of greater than0 to about 10.